The present invention relates in general to heating, ventilating and air-conditioning (HVAC) and, more particularly, to control of a fan powered terminal unit wherein the fan air flow or cubic feet per minute (CFM) can be preset without regard for the installation specifics of the HVAC system in which the terminal unit is to be used. While the fan control will be described with reference to a fan powered terminal unit for which the present invention is initially being applied, it is to be understood that the fan control arrangement of the present application may be used in a variety of HVAC applications including, for example, venting hoods, exhaust fans, supply fans and fan coils.
Fan-powered terminal units which provide variable air volume (VAV) are used for both cooling and heating of perimeter zones of a building. The terminal units use the free heat derived from lighting, people and other equipment within the building by inducing this warmer air from a building core ceiling plenum space and recirculating it to rooms calling for heat. If additional heat is required, supplemental heating coils within the terminal units may be activated thus eliminating the need for a central source of warm air.
Once a HVAC system is installed, it must be set-up by setting the terminal units to provide required air flow for the system. A portion of this set-up currently includes placing a flow measuring hood over an air outlet or diffuser and going into the ceiling to adjust an associated VAV terminal unit to obtain the proper air flow. This portion of the HVAC system set-up adds substantially to the cost with labor related costs currently running around $40 to $60 dollars per terminal unit.
An electronically commutated motor (ECM) is commercially available from General Electric which can provide a fixed air flow for a terminal unit regardless of static pressure provided the static pressures are within a permissible range. The ECM motor is controlled using a pulse width modulation (PWM) control signal with the pulse width being proportional to the air flow which is to be delivered by the terminal unit. Unfortunately, the width of the pulses of the PWM signal can not be readily determined without equipment which is not normally available to manufacturing personnel and HVAC contractors. Accordingly, while the ECM motors offer the promise of being able to preset the air flow for terminal units on the manufacturing floor before shipment and also once installed to accommodate changing conditions of a HVAC system, terminal units currently using ECM motors must still undergo the high cost air flow balancing procedures.
Accordingly, there is a need for an improved control arrangement for fans used in fan-powered terminal units which permit the air flow of the terminal units to be factory preset and reset without the conventional labor intensive balancing procedures currently required. Preferably, the fan control arrangement could be used for a variety of HVAC applications such as venting hoods, exhaust fans, supply fans and fan coils.
The present invention meets this need by providing an improved open loop control arrangement for fans in fan-powered terminal units which permit the air flow of the terminal units to be factory preset and reset using a voltmeter. The fan is responsive to the pulse width of pulses of a pulse width modulated signal to provide an air flow which is directly proportional to the pulse width. By adjusting the pulse width, the air flow may be set as desired. A pulse width modulated signal having pulses with a set amplitude and frequency is generated. The direct current (dc) voltage of the pulse width modulated signal is measured using a voltmeter. As the pulses have a set amplitude and frequency, the width of the pulses may be adjusted by controlling the dc voltage of the pulse width modulated signal. The fan is programmed to deliver the set air flow over a range of static pressures.
According to a first aspect of the present invention, a method of operating a fan motor in a ventilation system is provided. The fan motor is responsive to the width of pulses of a pulse width modulated signal to provide an air flow corresponding to the pulse width. The method comprises generating a pulse width modulated signal with pulses having a set amplitude. The width of the pulses is adjusted by adjusting the dc voltage of the pulse width modulated signal so that the fan motor provides a predetermined air flow.
The step of adjusting the width of the pulses by adjusting the dc voltage of the pulse width modulated signal so that the fan motor provides a predetermined air flow may be performed manually or automatically. The step of generating the pulse width modulated signal with the pulses having a set amplitude may comprise generating a periodic waveform having a predetermined frequency and a varying amplitude, generating a control signal having a selectable amplitude, and comparing the waveform with the control signal such that the pulses are defined by the portions of the waveform which are less than or equal to the selectable amplitude of the control signal. Preferably, the waveform is a triangular waveform.
The step of adjusting the width of the pulses by adjusting the dc voltage of the pulse width modulated signal so that the fan motor provides a predetermined air flow may comprise the step of controlling the selectable amplitude of the control signal. Preferably, the fan motor provides the predetermined air flow over a range of static pressures. The method may further comprise the step of measuring the dc voltage of the pulse width modulated signal using a digital voltmeter. Preferably, the predetermined frequency of the periodic waveform and the set amplitude of the pulses are substantially constant.
According to another aspect of the present invention, a method of operating a fan motor in a ventilation system is provided. The fan motor is responsive to the width of pulses of a pulse width modulated signal to provide an air flow corresponding to the pulse width. The method comprises generating a pulse width modulated signal with pulses having a set amplitude. A dc voltage of the pulse width modulated signal is measured with a voltmeter. The width of the pulses is adjusted by adjusting the dc voltage of the pulse width modulated signal so that the fan motor provides a predetermined air flow.
The step of adjusting the width of the pulses by adjusting the dc voltage of the pulse width modulated signal so that the fan motor provides a predetermined air flow may be performed manually or automatically. The step of generating a pulse width modulated signal with pulses having a set amplitude may comprise generating a periodic waveform having a predetermined frequency and a varying amplitude, generating a control signal having a predetermined amplitude, and comparing the waveform with the control signal such that pulses are defined by the portions of the waveform which are less than or equal to the predetermined amplitude of the control signal. Preferably, the waveform is a triangular waveform. The step of adjusting the width of the pulses by adjusting a dc voltage of the pulse width modulated signal so that the fan motor provides a predetermined air flow may comprise the step of controlling the predetermined amplitude of the control signal. Preferably, the fan motor provides the predetermined air flow over a range of static pressures. Preferably, the predetermined frequency of the periodic waveform and the set amplitude of the pulses are substantially constant.
According to yet another aspect of the present invention, a method of presetting the air flow generated by a fan motor for a ventilation system for operation within a range of static pressures is provided. A fan motor is provided which is responsive to the width of pulses of a pulse width modulated signal with the width corresponding to the air flow provided by the fan motor. The pulse width modulated signal is generated and the air flow provided by the fan motor is set by adjusting the width of the pulses by using a voltmeter to measure the dc voltage of the pulse width modulated signal, such that the air flow provided by the fan motor is set for static pressures within the range. Preferably, the step of setting the air flow provided by the fan motor by adjusting the width of the pulses by using a voltmeter to measure the dc voltage of the pulse width modulated signal is performed prior to installation of the ventilation system.
According to a further aspect of the present invention, an apparatus for circulating air in a ventilation system comprises a fan motor and a controller. The fan motor is responsive to the width of pulses of a pulse width modulated signal with the width corresponding to an air flow provided by the fan motor. The controller generates the pulses of the pulse width modulated signal. The pulses have a set amplitude and are coupled to the fan motor so that the width of the pulses can be determined by measuring a dc voltage of the pulse width modulated signal for setting the fan motor to provide a predetermined air flow.
The controller may comprise a voltage generator generating a control signal having a selected amplitude, a waveform generator generating a periodic waveform having a predetermined frequency and a varying amplitude, and a comparator generating the pulse width modulated signal in response to the waveform and the control signal, such that the pulse width of the pulses is proportional to the amplitude of the control signal. Preferably, the waveform comprises a triangular waveform and the comparator compares the waveform and the control signal such that the pulses are defined by the portions of the waveform which are less than or equal to the selected amplitude of the control signal.
The voltage generator may further comprise a voltage adjuster for selecting the amplitude of the control signal. The voltage adjuster may comprise a variable resistor or an interface to a control system programmed to automatically select the amplitude of the control signal. The voltage adjuster may further comprise a switching device for selecting one of the variable resistor and the interface to a control system for selecting the amplitude of the control signal. Preferably, the fan motor is an electrically commutated motor and the predetermined air flow is substantially constant over a predetermined range of static pressures. Preferably, the predetermined frequency of the periodic waveform and the set amplitude of the pulses are substantially constant.
According to a still further aspect of the present invention, a controller for controlling the air flow provided by a fan motor in a ventilation system is provided. The fan motor is responsive to the width of pulses of a pulse width modulated signal with the pulse width corresponding to the air flow provided by the fan motor. The controller comprises a voltage generator generating a control signal having a substantially constant predetermined amplitude, a waveform generator generating a periodic waveform having a predetermined frequency and a varying amplitude, and a comparator generating the pulse width modulated signal in response to the waveform and the control signal such that the width of the pulses is proportional to the amplitude of the control signal. Preferably, the predetermined frequency of the periodic waveform and the set amplitude of the pulses are substantially constant.
Preferably, the waveform comprises a triangular waveform and the comparator compares the waveform and the control signal such that the pulses are defined by the portions of the waveform which are less than or equal to the predetermined amplitude of the control signal. The voltage generator may comprise a voltage adjuster for selecting the amplitude of the control signal. The voltage adjuster may comprise a variable resistor or a processor programmed to automatically select the amplitude of the control signal. The voltage adjuster may further comprise a switching device for selecting one of the variable resistor and the processor for selecting the amplitude of the control signal.
Accordingly, it is an object of the present invention to provide an improved control arrangement for fans used in fan-powered terminal units which permit the air flow of the terminal units to be factory preset and reset without the conventional labor intensive balancing procedures currently required. It is another object of the present invention to factory preset and reset the air flow of terminal units using a voltmeter. It is yet another object of the present invention to provide a fan control arrangement which may be used for a variety of HVAC applications such as venting hoods, exhaust fans, supply fans and fan coils. Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.